This invention relates to a fuel injector for use in delivering fuel under pressure to a combustion space of an internal combustion engine. In particular the invention relates to a fuel injector of the electromagnetically actuable type suitable for use in a common rail type fuel system arranged to deliver diesel fuel to a compression ignition internal combustion engine.
A known fuel injector for use in such a fuel system is illustrated in FIG. 1 and comprises a valve needle 10 slidable within a bore 11. The needle 10 includes a surface exposed to the fuel pressure within a control chamber 12. The control chamber 12 is supplied with fuel from a supply passage 13 through a restriction 14, thus fuel is only permitted to flow to the control chamber 12 at a restricted rate. An electromagnetically actuable control valve 15 controls communication between the control chamber 12 and a chamber 16 which communicates with a low pressure drain reservoir through a backleak passage which is common to several injectors. The injector of FIG. 1 will be described in greater detail below.
Reliable, consistent operation of the control valve 15 is important to achieve as inconsistencies in the operation of the control valve may result in undesirable variations in the quantity of fuel injected and in the timing of fuel injection. Pressure waves may be transmitted to the control chamber 16 from other identical injectors via the common backleak passage. It will be appreciated that the application of pressure waves to the chamber 16 may impair the performance of the valve. It is an object of the invention to provide an injector in which this disadvantage is obviated or mitigated.
According to the present invention there is provided a fuel injector comprising a valve needle slidable within a bore, a surface associated with the needle being exposed to the fuel pressure within a control chamber, an electromagnetically actuable control valve controlling communication between the control chamber and a low pressure chamber, and a damping arrangement arranged to damp pressure waves applied to the low pressure chamber.
The damping arrangement conveniently comprises a volume which communicates with the low pressure chamber, the volume containing gas, in use. The gas, for example air, fuel vapour or a mixture thereof, is readily compressible and acts to damp pressure waves applied to the low pressure chamber.
The volume is conveniently defined by a blind drilling orientated, in use, with its blind end uppermost to retain the gas therein. The drilling conveniently extends adjacent part of the actuator for the control valve.